The tavern is independent of other buildings, but the troop-queue is not. Both the length of the troop line and the throughput speed depend on the level of the barrack, stable and Catapult workshop.
With each level of barack, stable and Catapult workshop you get the same percentage bonus per level tavern. But 1% of the increased queue at a level 100 barrack is more than 1% of the troopqueue of a 73 level barack.
This is also the case with the resource bonuses. The bonus is more effective at a level 100 quarry.